On the formation of oceanic detachment faults and their influence on intra-oceanic subduction initiation: 3D thermomechanical modeling

Abstract

Extensional detachment faults, which have been widely documented in slow-spreading and ultraslow-spreading ridges on Earth, can effectively localize deformation due to their weakness. After the onset of oceanic closure, these weak oceanic detachments may directly control the nucleation of a subduction zone parallel to the former mid-ocean ridge, as is suggested for the Neotethys in Middle Jurassic times. So far, this hypothesis has only been tested by 2D numerical models, whereas the geometry of detachment faults is intrinsically three-dimensional. Here, we conducted a series of 3D numerical thermomechanical experiments in order to investigate the formation of detachment faults in slow oceanic spreading systems and their subsequent response upon inversion from oceanic spreading to convergence.Numerical results show that during the oceanic spreading stage, the formation of detachment faults strongly depends on the magnitude of the healing rate of faulted rocks in the oceanic lithosphere, that reflects the stability of hydrated minerals along fractured rocks. The detachment faults formed in our 3D numerical models deviate from the "rolling hinge model" of oceanic detachment faulting where fault footwalls are rotated and oceanic core complexes are thereby formed. Our results accentuate that the controlling physical parameters for the development of oceanic core complexes and detachment faults can differ, and that their coupled development in nature remains a key target for future research.Upon modelled transition to compression, previously formed asymmetric spreading patterns are prone to asymmetric inversion, where one oceanic plate thrusts under the other. Our results suggest that detachment faults accommodate significant amounts of shortening during the initiation of oceanic closure, but, in contrast to the previously proposed simple conceptual model, no direct inversion of a single detachment fault into an incipient subduction zone is observed. Instead, a widespread interaction of multiple detachment faults occurs after the onset of convergence. Ultimately, the nascent subduction zone

Deformation mechanisms in mafic amphibolites and granulites: record from the Semail metamorphic sole during subduction infancy

“…1f; see Soret et al, 2017, for details). The preservation of prograde chemical zoning (over a dT ≥ 100 • C and a dP ≥ 0.1 GPa) suggests fast exhumation of the HT sole (≤ 1-2 Ma) after reaching peak conditions at 95-96 Ma, as supported by radiometric dating (e.g., Hacker, 1990;Rioux et al, 2016).…”

Seafloor expression of oceanic detachment faulting reflects gradients in mid-ocean ridge magma supply

“…At the same time, we allow the plastic strain in the fault zone to heal so that fault strength (cohesion) recovers over a timescale of 20 kyr. These models contrast with prior models that additionally included an evolving coefficient of friction in fault zones (Gerya, 2013;Püthe and Gerya, 2015;Liao and Gerya, 2015;Gülcher et al, 2019).…”

“…Third, we simplify spontaneous brittle faulting by reducing only cohesion with increasing strain and assuming a constant fracture healing rate. Recently, Gülcher et al (2019) demonstrated that the development of individual OCCs is strongly controlled by fracture healing rates, and their numerical results deviate significantly from the classic "rolling hinge" model of detachment faulting. Thus, there is a need for future studies that identify the most appropriate numerical approaches to fault strength evolution.…”

Deformation mechanisms in mafic amphibolites and granulites: record from the Semail metamorphic sole during subduction infancy

“…Dissolution-precipitation creep and associated amphibole-forming reactions may also control strain localization, and therefore the development of long-lived oceanic detachments and core complexes in slow-spreading environments (Boschi et al, 2006;Escartin et al, 2003;Gülcher et al, 2019), as well as continental crustal-scale shear zones in collisional settings under cooling conditions and exhumation (Getsinger et al, 2013;Giuntoli et al, 2018;Tatham et al, 2008).…”